U.S. Pat. No. 3,763,330 suggests an auxiliary device connectable to a cassette tape recorder by a cassette-shaped plug containing a transducer to allow electrical communication between the host and the auxiliary device. The auxiliary device can then record and play back from magnetic tapes on planar cards or some other tape recording medium different from the one used by the host. The auxiliary device has to be switched into the corresponding mode of the host so that both operate in either record or playback modes.
This invention involves recognition of a way for automatically switching an auxiliary or accessory device to a mode of operation corresponding to the mode of the host recorder/player so that an operator only has to press buttons or adjust switches on the host, and the auxiliary or accessory device automatically conforms to the mode of operation set for the host. This prevents any accidental mismatch between the host and the accessory, and makes the operation of these devices simpler and more convenient. The invention also aims at reliability, economy, and efficiency in circuitry for an accessory for a host tape recorder.